Light emitting device

ABSTRACT

A light emitting device includes a substrate, a light emitting element, and a plurality of bumps. The light emitting element is mounted on the substrate. The bumps connect the substrate and the light emitting element. The bumps are arranged in a plurality of columns extending parallel to one side of an outer edge of the light emitting element. A distance between adjacent ones of the bumps in one of the columns arranged closest to the outer edge of the light emitting element is smaller than a distance between adjacent ones of the bumps arranged on an inner side of the light emitting element in a plan view.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.15/841,769 filed on Dec. 14. 2017. The present application claimspriority to Japanese Patent Application No. 2016-254851, filed on Dec.28, 2016. The entire disclosures of U.S. patent application Ser. No.15/841,769 and Japanese Patent Application No. 2016-254851 are herebyincorporated herein by reference.

BACKGROUND

The present invention relates to a light emitting, device.

Improvements in the crystal quality of light emitting diodes made itpossible to increase the output and the luminance. As a consequence,they are utilized in various areas, such as general illumination andautomotive lighting applications, and further quality improvements havebeen proposed.

For example, there is known a light emitting element having a structurein which the n-type electrode connected to the n-type semiconductorlayer, which is exposed from the p-type semiconductor layer and theemission layer, is disposed on the p-type semiconductor layer via aninsulation film in order to achieve high luminance and good luminancedistribution. See, for example, Japanese Unexamined Patent ApplicationPublication Nos. 2015-192099 and 2014-207267.

SUMMARY

One object of an embodiment of the present invention is to provide alight emitting device capable of achieving good luminance distributionand a method for manufacturing the same.

A light emitting device according to one embodiment includes asubstrate, a light emitting element, and a plurality of bumps. The lightemitting element is mounted on the substrate, The bumps connect thesubstrate and the light emitting element. The bumps are arranged in aplurality of columns extending parallel to one side of an outer, edge ofthe light emitting element. A distance between adjacent ones of thebumps in one of the columns, arranged closest to the outer edge of thelight emitting element is smaller than a distance between adjacent onesof the bumps arranged on an inner side of the light emitting element ina plan view.

According to the present invention, a light emitting element capable ofachieving good luminance distribution can he provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic perspective view of one embodiment of the lightemitting device according to the present invention.

FIG. 1B is a cross, sectional view taken along line A-A′ in FIG. 1A.

FIG. 2A is a schematic plan view of the light emitting element used inthe light emitting device in FIG. 1A.

FIG. 2B is a partial cross sectional view taken along line B-B′ in FIG.2A.

FIG. 3 is a schematic plan view of another light emitting element usedin the light emitting device according to the present invention.

FIG. 4A is a schematic enlarged plan view for explaining a substratepreparation step in the method for manufacturing a light emitting deviceaccording to the present invention.

FIG. 4B is a schematic enlarged plan view for explaining a bump formingstep in the method for manufacturing a light emitting device accordingto the present invention.

FIG. 4C is a schematic enlarged plan view for explaining an elementmounting step in the method for manufacturing a light emitting deviceaccording to the present invention.

FIG. 4D is a schematic enlarged plan view for explaining a step ofdisposing a light transmissive member in the method for manufacturing alight emitting device according to the present invention.

FIG. 4E is a schematic enlarged plan view for explaining a cover memberforming step in the method for manufacturing a light emitting deviceaccording to the present invention.

FIG. 4F is a schematic enlarged plan view for explaining a cover memberforming step in the method for manufacturing a light emitting deviceaccording to the present invention.

FIG. 4G is a schematic enlarged plan view for explaining a cover memberforming step in the method for manufacturing a light emitting deviceaccording to the present invention.

FIG. 5 is a schematic plan view of a comparative light emitting element.

DETAILED DESCRIPTION OF THE EMBODIMENTS

One embodiment for practicing the present invention will be explainedbelow with reference to the accompanying drawings. The embodimentdescribed below, however, is an illustration for the purpose ofembodying the technical, concept of the present invention, and does notlimit the present invention. The sizes of the members and theirpositional relationship shown in each drawing might, be exaggerated forclarity of the explanations. Furthermore, the same designations andreference numerals represent members that are identical or similar innature as a rule, and redundant explanations are omitted whenappropriate.

Light Emitting Device

The light emitting device 10 related to the present embodiment, as shownin FIGS. 1A and 1B, includes a substrate 11, a light emitting element20, and a cover member 13.

The substrate 11, as shown in FIGS. 1B, 4A, and 4B, has a wiring pattern14 on its upper face. On the wiring pattern 14, first bumps 15 andsecond bumps 16 are arranged, and the light emitting element 20 isflip-chip mounted via the first bumps 15 and the second bumps 16.Moreover, on the substrate 11, the cover member 13 that covers the lightemitting element 20, the first humps 15, and the second bumps 16 isdisposed.

The light emitting element 20, as shown in FIG. 2B, includes asemiconductor stack 23 which successively has a first semiconductorlayer 21, an emission layer, and a second semiconductor layer 22 as wellas having a plurality of exposed portions 21 a exposing the firstsemiconductor layer 21 from the second semiconductor layer 22 on theupper face side of the second semiconductor layer 22; an insulation film24 which covers the semiconductor stack 23 and has openings 24 a abovethe plurality of exposed portions 21 a; a first electrode 25 connectedto the exposed portions 21 a at the bottom face of the openings 24 a andpartially disposed on the second semiconductor layer 22 via theinsulation film 24; and a second electrode 26 connected onto the secondsemiconductor layer 22.

The bumps include the first bumps 15 bonded to the first electrode 25,and the second bumps 16 bonded to the second electrode 26. In a planview, the first bumps 15 are spaced apart from the exposed portions 21a, and include two types having different surface areas.

The light emitting element 20 includes a plurality of exposed portionswhere the first semiconductor layer is exposed from the secondsemiconductor layer on the upper face side of the second semiconductorlayer in the semiconductor stack 23. If the exposed portions and thefirst bumps are arranged to overlap one another, i.e., if the firstbumps are disposed directly above the exposed portions 21 a, the impactof flip chip mounting might cause a crack to form in the insulationfilm. It is preferable to position the first bumps apart from theexposed portions in a plan view so that the cracks, are not allowed toform in the insulation film. In the light emitting device 10, the firstbumps 15 include large and small bumps, having different surface areas.Thus, a large number of first bumps can be densely arranged on the firstelectrode while avoiding the positions immediately above the exposedportions. This reduces the chances of localizing the current density tobe supplied to the light emitting element, thereby reducing illuminancevariance.

Furthermore, the high-density arrangement of the bumps directly underthe light emitting element can increase the paths for dissipating theheat generated by the light, emitting element during emission throughthe substrate via the bumps. The high-density arrangement facilitatesthe flow of the uncured resin material used for forming the cover memberbetween the light emitting element and the substrate when the covermember covering the lateral faces of the light emitting elements and thebumps is formed cm the substrate, reducing the chances of void formationor the like directly under the light emitting element. This can preventlight from leaking from the lower face of the light emitting element, aswell as effectively preventing the light emitting element fromseparating from the substrate which would otherwise be caused by theexpansion of a void as the temperature surrounding the light emittingdevice changes. Thus, a higher quality light emitting device can beprovided.

Substrate 11

The substrate 11 has a wiring pattern 14 on the upper face thereof, aridthe light emitting element 20 is flip-chip mounted on the wiring pattern14 via bumps 15 and 16. Examples of the substrate materials includeinsulating materials, such as a glass fiber reinforced epoxy, resins,and ceramics, as well as a metal material with an insulating materialformed on the surface thereof. Among all, a ceramic material which ishighly heat resistant and weather resistant is preferable for thesubstrate. Ceramics materials include alumina, aluminum nitride, and thelike.

The substrate 11 has multiple wiring patterns 14 on the upper surfacethereof.

Such a wiring pattern 14 may be anything that can supply electriccurrent to the light emitting element, and can be formed using anymaterial, thickness, or shape ordinarily employed in the art.Specifically, the wiring pattern 14 can be formed, for example, using ametal, such as copper, aluminum, gold, silver, platinum, titanium,tungsten, palladium, iron, nickel, or the like, or an alloy containingthese. Particularly, the outermost surface of the wiring pattern formedon the upper face of the substrate is preferably covered with a highlyreflective material, such as silver or gold, in order to efficientlyextract light from the light emitting element 20. The wiring pattern canbe Mimed by electroplating, electroless plating, vapor deposition,sputtering, or the like. In the case of using Au bumps for mounting thelight emitting element on the substrate, for example, using Au as theoutermost surface of the wiring pattern can improve the bonding betweenthe substrate and the substrate.

The wiring pattern 14 preferably has a pair of positive, and negativepatterns on the upper face of the substrate 11. Such wiring patternallows for the connection of the first electrode of the firstsemiconductor layer and the second electrode of the second semiconductorlayer in the light emitting element by way of flip chip mounting. Thewiring pattern 14 may be disposed not only on the upper surface of thesubstrate 11, but also inside and/or on the lower surface thereof.

Bumps 15 and 16

The wiring pattern 14 has, on the upper, surface, first bumps 15 to beconnected to the first electrode, and second bumps 16 to be connected tothe second electrode, of the light emitting element used for flip chipmounting of the light emitting element described later. Multiple bumpsare disposed for each. In the present embodiment, the first bumps 15, asshown in FIG. 4B, include two types having different surface areas.Examples of the plan view shapes of the bumps include a circular shape,substantially circular shape, or the like. The two Hypes of first bumpshas hg different surface areas include first huge bumps 155, and firstsmall bumps 15S each having a smaller surface area than a first largebump 15B. The second bumps 16 may have a different size from the firstbumps 15, but preferably have a similar size to that of the first largebumps 15B. The surf ice areas of the two types of first bumps 15 areappropriately set in accordance with the size or the like of the lightemitting element used. From the standpoint of heat, dissipation andbonding strength, the larger the total bump surface area bonded to asingle light emitting element, the more preferable it is. Consideringthe layout of the exposed portions, however, the length of the longestline segment (e.g., the diameter in the ease of a circular shape) ofeach first large bump 15B is preferably smaller than the distancebetween the centers of two adjacent exposed portions. It is preferablefor the first small bumps 15S to each have about 30 to 70% of thesurface area of each first large bump. This allows the first small bumpsto be disposed in the regions where the first huge bumps cannot bedisposed, thereby increasing the total bump surface area.

By providing the first bumps having two different surface areas in thismanner, the bumps can be densely arranged on the surface of the lightemitting element without overlapping the exposed portions arranged onthe semiconductor stack. This can distribute the current densitysupplied to the light emitting element, thereby attenuating luminancevariance.

In the case where the light emitting element 20 has a rectangular planview shape, in particular, it is preferable to arrange the first smallbumps 15S at least in the vicinity of two opposing sides of therectangular shape, along the sides. They may he arranged in the vicinityof each side of the two pairs of opposing sides, along each side. Such alayout enables uniform injection of electric current even in thevicinity of the perimeter of the light emitting element, therebyachieving an even more uniform luminance distribution and ensuringuniform in-plane heat dissipation.

The two types of first bumps having different surface areas may haveabout the same height, or have different heights. For example, the firstlarge bumps 15B preferably have a larger height than the first smallbumps. Since the first small bumps 15S are arranged in narrow regions inthe regions where the first large bumps 15B cannot be disposed, givingthem a lower height than the first large bumps 15B can reduce the impactresulting from bonding as compared to that applied to the first largebumps 15B, thereby more effectively preventing the bumps from beingcrushed and expanding their surface areas.

Although the first large bumps 15B and the first small bumps 15S may beregularly or randomly arranged, they are preferably regularly arrangedso that the current density supplied to the light emitting element 20would not be localized.

The first bumps 15 and the second bumps 16 can be formed with, forexample, gold, silver, copper, tin, platinum, zinc, nickel, or theiralloys, and can be formed by using, for example, stud bumps known in theart. Stud humps can be formed using a stud bump bonder, wire bondingapparatus, or the like.

Light Emitting Element 20

The light emitting, element 20, as shown in FIG. 2B, has a semiconductorstack 23 in which a first semiconductor layer 21, an emission layer, anda second, semiconductor layer 22 are stacked in that order, aninsulation film 24, a first electrode 25, and a second electrode 26. Thesemiconductor stack 23 has, on the upper face side of the secondsemiconductor layer 22, a plurality of exposed portions 21 a exposingthe first semiconductor layer 21 from the second semiconductor layer 22on the upper face side of the second semiconductor layer 22. Theinsulation film 24 covers the semiconductor stack 23, and has openings24 a above the plurality of exposed portions 21 a. The first electrode25 is connected to the exposed portions 21 a at the openings 24 a, andis partly disposed on the second semiconductor layer 22 via theinsulation film 24. The second electrode 26 is electrically connected tothe second semiconductor layer 22, and is disposed on the secondsemiconductor layer 22.

Examples of the plan view shapes of the light emitting element and/orthe semiconductor stack include polygons, such as a rectangle orhexagon, a polygon with rounded corners, circle, ellipse, or the like.

Semiconductor Stack 23

The semiconductor stack 23 is formed by successively stacking a firstsemiconductor layer 21 (e.g., n-type semiconductor layer), an emissionlayer, and a second semiconductor layer 22 (e.g., p-type semiconductorlayer) on a growth substrate 27. In the state of being incorporated in alight emitting element 20, however, the semiconductor stack can be onefrom which the growth substrate 27 has been removed.

Examples of the first semiconductor layer, the emission layer, and thesecond semiconductor layer include various semiconductors, such as groupIII-V compound semiconductors, group II-VI compound semiconductors, andthe like. Specific examples include nitride-based semiconductormaterials such, as In_(X)Al_(Y)Ga_(1-X-Y)N (0≤X, 0≤Y, X+Y≤1); InN, AlN,GaN, InGaN, AlGaN, InGaAlN, or the like can be used. Any film thicknessor layer structure known in the art can he used for each layer.

Growth Substrate 27

For the growth substrate 27, any that allows for epitaxial growth of thesemiconductor layers can be used. Examples of such growth substratematerials include insulating substrates, such as sapphire (Al₂O₃),spinet (MgAl₂O₄), or the like.

Exposed Portions 21 a

The semiconductor stack 23 has multiple exposed portions 21 a where thesecond semiconductor layer 22 and the emission layer are removed acrosstheir entire thicknesses, exposing the first semiconductor layer 21 fromthe second semiconductor layer and the emission layer. In other words,the semiconductor stack 23 has holes on the surface on the secondsemiconductor layer side, and the first semiconductor layer 21 isexposed at the bottom faces of the holes. The second semiconductor layer22, the emission layer, and the first semiconductor layer 21 are exposedat the lateral faces of the holes.

Although the shape, the size, the positions, and the number of theexposed portions can be appropriately set in accordance with theintended size, shape, electrode pattern, or the like of the lightemitting element, multiple exposed portions are preferably formed on theinner side of the edges of the semiconductor stack. The exposed,portions are preferably disposed in a regular sequence. This canattenuate illuminance variance of the light emitting element therebyallowing light to be uniformly extracted.

The exposed portions 21 a are electrically connected to the firstelectrode described later. The first electrode connected to the exposedportions is formed on the second semiconductor layer via the insulationfilm 24 discussed later. Such exposed portions are preferably arrangedso as to be spaced apart from one another in a plan view, morepreferably arranged in a regular sequence while maintaining a certaindistance from one another. The exposed portions may all have the sameshape and size, may individually or some of them may have differentshapes and sizes. However, the exposed portions preferably have aboutthe same size and shape. Since the exposed portions are the regionshaving no emission layer, regularly arranging multiple exposed regionsof about the same size can attenuate localization of the emission areaor the amount of the electrical current supplied. As a result, luminancevariance of the light emitting element can be attenuated as a whole.

Examples of the shapes of the exposed portions include a circle,ellipse, or polygon, such as a triangular, rectangular, or hexagonalshape, or the like. Among all, a circular shape, or substantiallycircular shape (e.g., ellipse or polygon with at least six sides) ispreferable. The size of the exposed portions can be appropriatelyadjusted based on the size of the semiconductor stack and the output,luminance, or the like of the light emitting element desired. The sizeof about several ten to several hundred um in diameter, for example, ispreferable. From another perspective, the diameter is preferably about1/20 to ⅕ of a side of the semiconductor stack.

The total area of the exposed portions arranged on the inner side of theedges of the semiconductor stack is preferably 30% at most, 25% at most,18% at most, or 15% at most of the surface area of the semiconductorstack. Setting the total area in these ranges can attain balance in theelectric current supplied to the light emitting element, therebyattenuating illuminance variance attributable to localization of thepower supplied.

Insulation Film 24

The insulation film 24 covers the upper face and the lateral faces ofthe semiconductor stack 23, and has openings 24 a above the exposedportions 21 a. Because the insulation film 24 covers the semiconductorstack 23 and have the openings 24 a above the exposed portions 21 a, thefirst electrode 25 can be formed over a more extensive area of the upperface of the insulation film 24.

The insulation film 24 is formed using a material and thickness capableof securing electrical insulation known in the art. Specifically, ametal oxide or metal nitride can be used for the insulation film 24; forexample, at least an oxide or nitride selected from the group consistingof Si, Ti, Zr, Nb, Ta, and Al can suitably be used.

First Electrode 25 and Second Electrode 26

The first electrode 25 and the second electrode 26 are disposed on theupper face side of the semiconductor stack (i.e., on the secondsemiconductor layer side opposite the growth substrate). The firstelectrode and the second electrode may be electrically connected to thefirst semiconductor layer and the second semiconductor layer,respectively, via the reflective electrode described later, instead ofbeing directly connected thereto.

The first electrode and the second electrode can be formed using metalssuch as Au, Pt, Pd, Rh, Ni, W, Mo, Cr, Ti, Al, Cu, or their alloys as asingle layer film or multilayered film. Specifically, these electrodescan be formed with a multilayered film, such as Ti/Rh/Au, Ti/Pt/Au,W/Pt/Au, Rh/Pt/Au, Ni/Pt/Au, Al—Cu alloy/Ti/Pt/Au, A;—Si—Xually/Ti/Pt/Au, Ti/Rh, or the like, stacked from the semiconductor layerside. Any film thickness used in the art can be employed.

The shapes of the first electrode and the second electrode, in the caseof a rectangular semiconductor stack, are preferably similarlyrectangular or substantially rectangular. The first electrode and thesecond electrode are preferably, arranged in parallel and alternately inone direction in a single semiconductor stack in a plan view. Forexample, it is preferable to arrange them so that the first electrodeinterposes the second electrode in a plan view.

The first electrode is electrically connected to the exposed portionsarranged on the second semiconductor layer side of the semiconductorstack described above. In this case, the first electrode is preferablyconnected so as to cover the exposed portions, more preferably connectedto all exposed portions integrally. Accordingly, the first electrode isdisposed not only on the first semiconductor, but also above the secondsemiconductor layer. In this case, the first electrode 25 is disposed onthe lateral faces (i.e., the lateral, faces of the emission layer andthe second semiconductor layer) of the holes that form the exposedportions and the second semiconductor layer via the insulation film 24.

The second electrode is disposed on the second semiconductor layer ofthe semiconductor stack described above, and is electrically connectedto the second semiconductor layer. The second electrode may be in directcontact with the second semiconductor layer, but is preferably disposedon the second semiconductor layer via the reflective electrode discussedlater.

Reflective Electrode

As shown in FIG. 2B, the light emitting element 20 has a reflectiveelectrode 28 interposed between the second electrode and the secondsemiconductor layer.

For the reflective electrode 28, silver, aluminum, or an alloy havingeither of these as a major component can be used, and silver or a silveralloy having high reflectance for the light emitted from the emissionlayer, in particular, is more preferable. The reflective electrode 28preferably has a thickness that can effectively reflect the lightemitted from the emission layer, for example, about 20 nm to 1 μm. Thelarger the contact area between the reflective electrode and the secondsemiconductor layer, the more preferable it is. Accordingly, it ispreferable to dispose the reflective electrode 28 also between the firstelectrode 25 and the second semiconductor layer 22. Specific examples ofthe total surface area of the reflective electrode 28 include at least50%, at least 60%, or at least 70% of the surface area of thesemiconductor stack.

In the case where the reflective electrode 28 contains silver, aprotective layer 29 that covers the upper face thereof, more preferablythe upper thee and the lateral faces thereof may be provided in order toprevent the migration of silver.

The protective layer 29 may be formed using a conductive material, suchas a metal, alloy, or the like, usually used as an electrode material,or may be formed using an insulating material. Examples of conductivematerials include a single layer or multilayered film containing ametal, such as aluminum, copper, nickel, or the like. Examples ofinsulating materials include those mentioned earlier With reference tothe insulation film 24. and SiN, among all, is preferably used. An SiNis a dense film and thus excels in preventing moisture penetration. Thethickness of the protective layer 29 is, for example, about severalhundred nm to several μm for effectively preventing silver migration.

In the case of forming the protective layer 29 with an insulatingmaterial, providing an opening in the protective layer 29 above thereflective electrode can achieve electrical connection between thereflective electrode and the second electrode.

In the case where the light emitting element 20 has the reflectiveelectrode 28 and the protective layer 29 on the second semiconductorlayer, the insulating film 24 that covers the semiconductor stack 23covers the reflective electrode 28 and the protective layer 29, and hasan opening directly under the second electrode 26 whereby the secondelectrode 26 and the reflective electrode 28 are electrically connected.

Cover Member 13

The cover member 13, as shown in FIG. 1B, covers the light emittingelement 20, the first bumps 15, the second bumps 16, and part of or theentire upper face of the substrate 11. Above all, the cover member 13preferably entirely covers the lateral faces of the light emittingelement 20, between the light emitting element 29 and the substrate 11,the upper face of the substrate 11, and the lateral faces of the firstbumps 15 and the second bumps 16.

The cover member 13 can be formed with a resin having light reflecting,transmitting, or light shielding properties, or any such resincontaining a light reflecting substance, phosphor, diffusing agent,coloring agent, or the like. Among all, the cover member preferably haslight reflecting and/or light shielding properties. Any resin, lightreflecting substance, and the like ordinarily used in the art can beused to structure the cover member.

Examples of resins include a resin containing one or more, or a hybridresin, of silicone resins, modified silicone resins, epoxy resins,modified epoxy resins, and acrylic resins. Examples of light reflectingsubstances include titanium oxide, silicon oxide, zirconium oxide,potassium titanate, alumina, aluminum nitride, boron nitride, mullite,and the like.

The material that structures the cover member 13 preferably includes aresin having high fluidity and is curable by heat or irradiation oflight from the standpoint of ease of penetration between the lightemitting element and the substrate, as well as void prevention. Such amaterial, for example, has fluidity indicated by the viscosity of 0.5 to30 Pa·s. Moreover, the amount of reflection and the amount oftransmittance can be varied by the content of the light reflectingsubstance or the like in the material that structures the cover member13. For example, the cover member preferably contains at least 20 wt %of a light reflecting substance.

The cover member 13 can be formed by, for example, injection molding,potting, resin printing, transfer molding, compression molding, or thelike.

Light Transmissive Member 17

As shown in FIG. 1A and FIG. 1B, the light emitting device 10 has alight transmissive member 17 on the light emitting element 20. The lightemitting element 20 is flip-chip mounted on the wiring pattern using theface having the first and second electrodes as the lower face. The lightemitting element 20 uses the opposing upper face as the principal lightextraction face which is bonded to the lower face of the lighttransmissive member 17.

The light transmissive member 17 covers the light extraction face of thelight emitting element and is capable of transmitting at least 50% or atleast 60%, preferably at least 70% of the light emitted by the lightemitting element to be externally released. The light transmissivemember can contain a light diffusing agent and/or a phosphor capable ofconverting the wavelength of at least part of the light emitted from thelight emitting element 20.

The lower face of the light transmissive member preferably has an areawhich is about 80 to 150% of the upper face area of the light emittingelement. The lower face perimeter of the light transmissive memberpreferably coincides with, or is positioned on the inside or the outsideof, the upper face perimeter of the light emitting element. In otherwords, in a plan view, one of the light emitting element's upper faceand the light transmissive member's lower face is preferably included inthe other. The thickness of the light transmissive member, for example,is 50 to 300 μm.

The light transmissive member can be formed with, for example, a resin,glass, inorganic material, or the like. Examples of light transmissivemembers containing a phosphor include a phosphor sintered body as wellas a resin, glass, or other inorganic material containing a phosphor.The light transmissive member may be a sheet-shaped molded resin, glass,inorganic material or the like, having a resin layer containing aphosphor formed on the surface thereof. The higher the transparency ofthe light transmissive member, the more reflection it achieves at theinterface with the cover member, thereby increasing the luminance.

Examples of the phosphors to be contained in the light transmissivemember include, in the case where a blue or ultraviolet light emittingelement is used as the light emitting element 20, cerium-activatedyttrium aluminum garnet-based phosphors (YAG:Ce); cerium-activatedlutetium aluminum garnet-based phosphors (LAG:Ce); europium- and/orchromium-activated nitrogen-containing calcium, aluminosilicate-basedphosphors (CaO—Al₂O₃—SiO₂:Eu); europium-activated silicate-basedphosphors ((Sr,Ba)₂SiO₄:Eu); nitride-based phosphors, such as β-SiAlONphosphors (e.g., Si_(6-Z)Al_(Z)O_(Z)N_(8-Z):Eu (0<Z<4.2)), CASN-basedphosphors, SCABN-based phosphors or the like; KSF-based phosphors(K₂SiF₆:Mn); sulfide-base phosphors, and quantum dot phosphors. Bycombining these phosphors with a blue or ultraviolet light emittingelement, light emitting devices of various emission colors (e.g., awhite light emitting device) can be produced. In the case of includingsuch a phosphor in the light transmissive member, the concentration ofthe phosphor is preferably, for example, about 5 to 50%.

The light transmissive member is bonded to cover the light extractionface of the light emitting element. The light transmissive member andthe light emitting element can be bonded via a bonding material 18. Forthe bonding material 18, any known resin, such as epoxy or silicone, canbe used. In bonding the light transmissive member to the light emittingelement, moreover, a direct bonding method, such as crimping, sintering,surface activated bonding, atomic diffusion bonding, or hydroxidecatalysis bonding, may alternatively be used.

In the case where the light emitting device 10 includes a lighttransmissive member 17, it is preferable to cover the lateral faces ofthe light transmissive member 17 in part or in whole with the covermember 13.

The light emitting device may optionally include other devices andelectronic parts, such as a protective device 19 or the like. Thesedevices and parts are preferably embedded in the cover member 13.

Method for Manufacturing a Light Emitting Device

The light emitting device according to the present embodiment primarilyhas a substrate preparation step, a bump forming step, a light emittingelement mounting step, and a cover member forming step. The materialsand layout of the members are as explained above with reference to thelight emitting device 10, and thus the explanations here will be omittedwhen appropriate.

Furthermore, a step of disposing a light transmissive member 17 on thelight emitting element 20 and a step of mounting electronic parts, suchas a protective device, can optionally be included prior to forming thecover member 13.

Substrate Preparation Step

A substrate 11 having a wiring pattern 14 formed on the upper facethereof is prepared. As shown in FIGS. 4A and 4B, the substrate 11simply needs to have on the surface thereof a wiring pattern 14, whichinclude a first wiring pattern 14 a to be connected to the firstelectrode of the light emitting element 20 and a second wiring pattern14 b to be connected to the second electrode of the light emittingelement 20, formed as the wiring pattern 14.

In order to simultaneously manufacture multiple light emitting devices,a collective body of the substrates 11 is preferably used. Using thecollective body of the substrates allows multiple light emitting devicesto be collectively formed, thereby increasing the production efficiency.The collective body of the substrates can ultimately be divided intoindividual light emitting devices as shown in FIG. 4G.

Bump Forming Step

As shown in FIG. 4B, two types or first bumps 15 having differentsurface areas, i.e., first small bumps 15S each having a small surfacearea and first large bumps 15B each having a larger surface area thanthe first small bumps, are formed on the first wiring pattern 14 a.Moreover, on the second wiring pattern 14 b, second bumps 16 are formed.The second bumps 16 can each have a give surface area, but arepreferably sized about the same as the first large bumps 15B or thefirst small bumps 15S for the purpose of increasing the productionefficiency. It is preferable to suitably select the site of the secondbumps by taking into consideration the plan view shape of the secondelectrode to be bonded so that the total surface area of the secondbumps is large.

The layouts of the bumps relative to the wiring pattern are determinedin accordance with the exposed portions, the electrode layout, or thelike of the light emitting element to be mounted thereon while enablingthe mounting of the light emitting element discussed later.

The first bumps and the second bumps can be formed by using, forexample, a commercially available stud bump bonder or wire bonder.Specifically, the tip of the metal wire fed through the capillary of astud bump bonder is melted to form a ball and the thrilled ball isbonded to a wiring pattern 14, followed by separating the bonded ballfrom the metal wire. Stud bumps are firmed on the wiring pattern in thismanner. It is preferable to separate a ball from the metal wire so thatthe upper end thereof is relatively flat by lifting the capillary whileholding the metal wire after bonding the ball onto a wiring pattern andparallel transferring the capillary thereby to allow the edge providedat the capillary tip to scrape and cut the deformed ball.

The surface area of a bump can be sized by suitably adjusting the amountof metal wire to be melted, the tip shape of the capillary, and thepressing force. A bump can have any height by suitably adjusting theheight to which capillary is lifted, the parallel transfer timing, orthe like. The upper end of a bump may alternatively be flattened byprocesses, such as etching, blasting, polishing, or the like. The tipend of a stud bump may be softened or smoothed by allowing the tip endto melt and recrystallize using sparks generated by applying a voltageto the formed stud hump.

The bumps having two different surface areas are formed by way of themethods described above. This can reduce the distance between the bumpsthereby highly densely arranging the bumps. Furthermore, softening theupper ends of the stud bumps allows the upper ends to be readilydeformed during flip chip mounting and facilitates bonding to theelectrodes of the light emitting element. This can achieve high-strengthbonding even at room temperature.

The intervals between the first bumps, and between the second bumps, canbe suitably set based on the size of the light emitting element, thenumber of bumps, or the like. For example, considering the fluidity ofthe resin material used in the cover member forming step describedlater, the distance between the second bumps 16 arranged in onedirection is preferably set smaller than the distance between the firstlarge bumps 15B arranged in the same direction. Similarly, the distancebetween the first small bumps arranged in the same direction ispreferably set smaller than the distance between the first large bumps.Specifically, the distance between the first large bumps 15B is, forexample, 20 to 50 μm, the distance between the second bumps 16 is, forexample, 0 to 20 μm, and the distance between the first small bumps 155is, for example, 50 to 80 μm.

From the heat dissipation standpoint, moreover, the larger the bondingarea between the bumps and the light emitting element, the morepreferable it is. For example, the total surface area of the first bumpsconnected to the first electrode is preferably at least 25% of thesurface area of the first electrode. The total surface area of thesecond bumps connected to the second electrode is preferably at least50% of the surface area of the second electrode.

Element Mounting Step

As shown in FIG. 4C, the light emitting element 20 is flip-chip mountedon the wiring pattern 14. The first electrode 25 and the secondelectrode 26 of the light emitting element 20 are bonded to the firstbumps 15 and the second bumps 16 respectively. In this case, the firstbumps 15 are arranged so that none of the first large bumps 15B and thefirst small bumps 15S overlap the exposed portions 21 a of the firstsemiconductor layer of the light emitting element 20 in a plan view.Arranging the bumps spaced apart from the exposed portions in thismanner can prevent cracks from forming in the light emitting element 20attributable to the pressing force applied to the light emitting elementwhen it is bonded onto the bumps. As shown in FIG. 2A and FIG. 2B, thefirst electrode 25 of the light emitting element 20 is formed on thesecond semiconductor layer via the insulation film 24. The insulationfilm 24 covers the semiconductor stack 23, and has the openings 24 aabove the exposed portions 21 a. The first electrode 25 is formed to beelectrically connected to the first semiconductor layer 21 at the bottomfaces of the openings 24 a, and to cover the lateral Ewes of the exposedportions 21 a (i.e., lateral faces of the holes that form the exposedportions 21 a) and the upper face of the second semiconductor layer viathe insulation film 24 that covers the semiconductor stack. In thesemiconductor stack 23, steps are formed by the surface of the secondsemiconductor layer and the exposed portions 21 a. If a large load isapplied to any of the steps, a crack might be formed in the lightemitting element 20. The metal oxide or metal nitride used to form theinsulation film 24, in particular, is hard, brittle, and thussusceptible to cracks, as compared to the metal material used to formthe electrodes. A crack occurring in the insulation film would allow thefirst electrode to be in electrical conduction with the secondsemiconductor layer, which would likely cause the light emitting element20 to have a short circuit. In other words, by arranging the bumpsspaced apart from the exposed portions in a plan view, the occurrence ofcracks in the insulation film 24 can effectively be avoided. Beingarranged spaced apart herein means that the outer edges of the bumps donot overlap the outer edges of the exposed portions in a plan view evenafter the light emitting element is pressed to be connected to the bumpswhere the pressure laterally expands the bumps to increase their surfaceareas.

In the case where the first small bumps 15S among the first humps arearranged in the vicinity of the two opposing sides of the light emittingelement 20, the expansion of the bumps' surface areas caused by thepressure applied when the bumps are bonded to the light emitting elementis smaller as compared to the first large bumps 15B. Thus, shortcircuits attributable to the laterally expanded bumps creeping onto thelateral faces of the light emitting element 20, or the like, can beavoided. Furthermore, even if the light, emitting element 20 is warped,setting a smaller height for the first small bumps 15S than that for thefirst large bumps allows the light emitting element to attain anappropriate pressure load, bump expansion, and connection with the bumpscorresponding to the warp.

Step of Disposing Light Transmissive Member

The method for manufacturing a light emitting device according to thepresent embodiment may have a step of disposing a light transmissivemember. In the step of disposing a light transmissive member, as shownin FIG. 4D, a light transmissive member 17 is disposed to cover theupper, face of the light emitting element. The light transmissive member17 can be disposed by using any transparent bonding material 18 known inthe art.

The step of disposing a light transmissive material may be performedbefore the element mounting step; for example, in the case of bondingthe light transmissive member and the light emitting element withoutusing a bonding material 18, the step of disposing a light transmissivemember is preferably performed before the element mounting, step.

Cover Member Forming Step

The cover member forming step is a step of forming a cover member 13 onthe substrate 11 that surrounds the light emitting element 20 which hasbeen mounted. The cover member 13 is formed to cover the lateral facesof the bumps at the lower face of the light emitting element 20, i.e.between the light emitting element 20 and the substrate 11. In the casewhere the light emitting device is provided With a light transmissivemember 17, the cover member 13 is formed to cover the lateral faces ofthe light transmissive. member 17. At this point, exposing the upperface of the light transmissive member 17 from the cover member 13produces a light emitting device 10 having the upper face of the lighttransmissive member 17 as the emission face.

The cover member 13 can be formed by placing a nozzle of a resindispenser above the substrate 11 and moving the nozzle while dispensingan uncured resin from the nozzle tip.

The cover menthes 13 is preferably formed in multiple resiftapplications.

First, as shown in FIG. 4E, the uncured resin material is dispensedbetween the multiple light emitting devices along the borders of thedevices'that ate arranged in rows and columns on the collective body ofthe substrates every other row or column, for example, at the positionindicated by the arrow in FIG. 4E. The resin material flows on thesubstrate 11 and under the light emitting element 20 while wetting andspreading over the substrate 11 as shown in FIG. 4F.

Next, the resin material is dispensed similarly between the rows orcolumns of the devices, one row or column at a time, for example, asindicated by the arrows in FIG. 4F, to cover the lateral faces of thelight emitting elements.

Supplying the resin material in two applications in this manner canreduce the occurrence of voids in the resin material disposed under thelight emitting elements. In other words, supplying the resin materialevery other row or column during the first application allows the resinto flow from one side, thereby allowing the air to escape to the otherside. After disposing the resin material under the light emittingelements, the resin material is supplied for the second dine to form theresin that rovers the lateral faces of the light emitting elements. Inthis manner, the resin material having fluidity can effectivelypenetrate into the space between the light emitting elements and thesubstrates.

Furthermore, the highly densely arranged bumps discussed earlierfacilitate the flow of the resin material along the narrow spacesbetween the bumps (the so-called capillary action), allowing the covermember to be formed in the appropriate locations in a simplified mannerwhile preventing the occurrence of voids.

In the present embodiment, moreover, the bumps are arranged so that thedistance between the bumps located in the center of each light emittingelement is shorter than the distance between the bumps located near theedges of the light emitting element along the direction of the flow ofthe resin material under the light emitting element, i.e., the directionperpendicular to the direction of the movement of the nozzle thatsupplies the resin material on the upper face of the substrate 11. Thisfacilitates the flow of the resin material in the center of each lightemitting element by utilizing the capillary action mentioned above,thereby reducing the occurrence of voids attributable to the resinmaterial infiltrating from the edges. In the present embodiment, alongthe direction perpendicular to the direction of the nozzle movement, thefirst small bumps 15S are arranged at the outermost locations, i.e.,near the edges of the substrate 11, while arranging the second bumps 16each having about the same size as that of the first large bumps 15B atthe innermost locations, i.e., in the vicinity of the center directlyunder the light emitting element, more densely than the first largehumps 15B.

Dividing Light Emitting Devices

As shown in FIG. 4G, the light emitting device 10 having a single lightemitting element 20 mounted thereon can be obtained by dividing thesubstrate 11 having the cover member 13 formed thereon along the dottedlines in FIG. 4G into individual light emitting devices 10. Thesubstrate can be divided by using any means known in the art, such as adicing saw.

Example 1

The light emitting device according to Example 1 was produced by usingthe method for manufacturing a light emitting device described in theforegoing, using a light emitting element 20 having, a plan view shapeof substantially a square, 1.0 mm per side.

As shown in FIG. 2A and FIG. 2B, the light emitting element 20 has asecond electrode 26 which has a narrow strip shape and is disposedvertically across the central portion of the element, and a firstelectrode 25 disposed on both sides of the second electrode 26. Thefirst electrode 25 located on both, sides of the second electrode 26 iscontinuous at both long side ends of the second electrode 26. In otherwords, the first electrode 25 is disposed to surround the narrow stripshaped second electrode 26. The width, i.e., the short side length, ofthe second electrode 26 is about 140 μm, and the width of the firstelectrode interposing the second electrode is about 370 μm on each side.Exposed portions 21 a of the first semiconductor layer are arrangedunder the first electrode 25. The exposed portions 21 a are eachsubstantially circular in shape having a diameter of 53 μm, and 7×3pieces of the exposed portions are arranged at equal intervals on eachside of the second electrode 26. The distance between two opposingexposed portions that interpose the second electrode 26 is, for example,0.28 μm, The distance from an edge of the semiconductor stack to theexposed portions that are closest to the edge is, for example, 0.07 μm.

In the substrate 11 having such a light emitting element 20 mountedthereon, the first bumps 15 are arranged at the positions spaced apartfrom and not overlapping the exposed portions 21 a in the state wherethe light emitting element 20 is mounted on the wiring pattern 14; forexample, at the positions indicated by the two-dot chain lines in thelight emitting element 20 shown in FIG. 2A. Among the first bumps, thefirst large bumps 15B are each arranged per region of the smallestsquare having the exposed portions 21 a at four corners. On the firstelectrode 25 in each of the regions on both sides of the secondelectrode, 6×2 pieces of the first large bumps 15B are disposed. Thefirst large bumps 15B are substantially circular in shape and about 100μm in diameter. The first small bumps 15S are arranged between theexposed portions 21 a arranged along the edges of the semiconductorstack, 6×1 pieces per side. The first small bumps 15S are substantiallycircular in shape and about 80 μm in diameter.

The second bumps 16, 8×1 pieces, are arranged at equal intervals alongthe second electrode 26 in the state where the light emitting element 20is mounted on the wiring pattern 14. The second bumps 16 are circular inshape and about 100 μm in diameter. The distance between two adjacentsecond bumps 16 is smaller than the distance between two adjacent firstlarge bumps 15 arranged in the same direction.

In the light emitting device according to Example 1, the surface area ofthe first electrode 25 is about 0.694 mm², and the total surface area ofthe first bumps is about 0.235 mm². Thus, the total surface area of thefirst bumps is about 34% of the surface area of the first electrode. Thesurface area of the second electrode 26 is about 0.120 mm², and thetotal surface area of the second bumps is about 0.063 mm². Thus, thetotal surface area of the second bumps is about 53% of the surface areaof the second electrode.

Example 2

The light emitting device according to Example 2 was produced by usingthe method for manufacturing a light emitting device described in theforegoing, using a light emitting element 30 having a plan view shape ofsubstantially a square, 0.8 mm per side.

As shown in FIG. 3, the light emitting element 30, similar to the lightemitting element 20 of Example 1, has a second electrode 56 which has anarrow strip shape and is disposed to divide the element in the middle,and a first electrode 55 which is disposed to surround the secondelectrode 56.

Exposed portions 31 a of the first semiconductor layer are disposedunder the first electrode 55. The exposed portions 31 a which aresubstantially circular in shape, 53 μm in diameter, are regularlyarranged at equal intervals, for example, with a distance between thecenters of two adjacent exposed portions of 0.16 mm, on both sides ofthe second electrode 56, 5×2 pieces each. The distance between thecenters of two opposing exposed portions that interpose the secondelectrode 56 is, for example, 0.28 mm. The distance from an edge of thesemiconductor stack to the centers of the exposed portions that areclosest to the edge is, for example, 0.007 mm.

In the substrate 11 having such a light emitting element 30 mountedthereon, the first bumps 35 and the second humps 36 are arranged at thepositions spaced apart from and not overlapping the exposed portions 21a in the state where the light emitting element 30 is mounted on thewiring pattern; for example, at the positions indicated by the two-dotchain lines in the light emitting element 30 shown in FIG. 3. Among thefirst bumps, the first large bumps 15B are each arranged per region ofthe smallest square having the exposed portions 21 a at four corners. Onthe first electrode 55 in each of the regions on both sides of thesecond electrode 56, 4×1 pieces of the first lame bumps 35B aredisposed. The first large bumps 35B are substantially circular in shapeand about 100 μm in diameter. The first small bumps 35S are arrangedbetween the exposed portions 21 a arranged along the edges of thesemiconductor stack, 4×1 pieces per side. Moreover, a piece of firstsmall bump 35S is arranged at each end of each column of the first largebumps 35B. The first small bumps 35S are substantially circular in shapeand about 80 μm in diameter.

The second bumps 36, 6×1 pieces, are arranged at equal intervals alongthe second electrode 56 in the state where the light emitting element 30is mounted on the wiring pattern. The second bumps 36 are circular inshape and about 100 μm in diameter. The distance between two adjacentsecond bumps 36 is smaller than the distance between two adjacent firstlarge bumps 35 which, are arranged in the same direction.

In the light emitting device according to Example 2, the surface area ofthe first electrode 55 is about 0.396 mm², and the total surface area ofthe first bumps is about 0.117 mm². Thus, the total surface area of thefirst bumps is about 30% of the surface area of the first electrode. Thesurface area of the second electrode 56 is about 0.089 mm², and thetotal surface area of the second bumps is about 0.048 mm². Thus, thetotal surface area of the second bumps is about 54% of the surface areaof the second electrode.

As a comparative example, as shown in FIG. 5, a light emitting devicewas prepared using a light emitting element 60 having 6×1 pieces ofsecond bumps 66 as opposed to the light emitting element 20. The lightemitting device of the comparative example has a similar construction tothat of Example 1 except for having no first small bumps and a fewernumber of second bumps 66.

Evaluation

The thermal resistance and the bump strength of the light emittingdevices of Example 1 and the comparative example were measured.

The results show that the thermal resistance (°C./W) decreased by 6.5%and the bonding strength (gf) between the light emitting element and thesubstrate increased by 4.5% as compared to the comparative example.

The light emitting device according to the present invention can be usedas a light source in various applications, such as for lightingfixtures, various indicators, automotive lights, displays, liquidcrystal display backlights, sensors, traffic lights, automotive parts,signage channel letters, and the like.

What is claimed is:
 1. A light emitting device comprising; a substrate;a light emitting element mounted on the substrate; and a plurality ofbumps connecting the substrate and the light emitting element, the bumpsbeing arranged in a plurality of columns extending parallel to one sideof an outer edge of the light emitting element, a distance betweenadjacent ones of the bumps in one of the columns arranged closest to theouter edge of the light emitting element being smaller than a distancebetween adjacent ones of the bumps arranged on, an inner side of thelight emitting element in a plan view.
 2. The light emitting deviceaccording to claim 1, wherein the bumps in the one of the columnsclosest to the outer edge of the light emitting element are arranged atequal intervals.
 3. The light emitting device according to claim 1,wherein the light emitting element includes a first electrode and asecond electrode arranged at a lower face of the light emitting element,and the bumps include a plurality of first bumps connected to the firstelectrode and a plurality of second bumps connected to the secondelectrode, the first bumps and the second bumps being arranged indifferent ones of the columns.
 4. The light emitting device according toclaim 3, wherein the first bumps include a plurality of first smallbumps and a plurality of first large bumps each having a larger surfacearea than each of the first small bumps, the first small bumps and thefirst large bumps being arranged in different ones of the columns. 5.The light emitting device according to claim 4, wherein a number of thefirst small humps arranged in one of the columns is the same as a numberof the first large bumps arranged in another of the columns.
 6. Thelight emitting device according to claim 4, wherein the first smallbumps are arranged in the one of the columns arranged closest to theouter edge of the light, emitting element.
 7. The light emitting deviceaccording to claim 3, wherein a number of the second bumps arranged inone of the columns is higher than a number of the bumps arranged M otherones of the columns.
 8. The light emitting device according to claim 3,wherein the first electrode is, arranged on both sides of the secondelectrode in the plan view.
 9. The light emitting device according toclaim 1, further comprising a light transmissive member disposed on thelight emitting element.
 10. The light emitting device according to claim9, wherein the light transmissive member contains a phosphor.
 11. Thelight emitting device according to claim 9, wherein a lower face of thelight transmissive member has an area of about 80 to 150% of an upperface area of the light emitting element.
 12. The light emitting deviceaccording to claim 1, further comprising a cover member covering thelight emitting element, the bumps, and the substrate.
 13. The light,emitting device according to claim 12, wherein the cover member containsa light reflective material.
 14. The light emitting device according toclaim 3, wherein a total surface area of the first bumps connected tothe first electrode is at least 25% of a surface area of the firstelectrode.
 15. The light emitting device according to claim 3, wherein atotal surface area of the second bumps connected to the second electrodeis at least 50% of a surface area of the second electrode.